This invention relates to a time data processing apparatus having a time-keeping circuit.
A calculator having a time-keeping circuit, such as an electronic calculator with an electronic clock, has been put to practical use. The time-keeping circuit and CPU (central processing unit) of such a known calculator operate independently of each other. It is therefore very difficult to write time data into the CPU from the time-keeping circuit while the CPU is carrying out various arithmetic operations using such time data. Thus, the known calculator is operated in the time-keeping mode at one time and in the calculation mode at another time. The time-keeping circuit is therefore considered to be no more than an attachment to the calculator. Further, such calculator cannot effect complicated arithmeticoperations. For example, it cannot add up the results of various arithmetic operations carried out during different periods of time.
Another known calculator with a time-keeping circuit starts effecting an arithmetic operation at a preset time. That is, it begins to carry out an arithmetic operation when the current time coincides with the preset time. To achieve this, the CPU of such calculator is periodically accessed to the time-keeping circuit (e.g. every second), thereby to detect the coincidence between the current time and the preset time. In this case, the shorter the time during which the CPU is accessed to the time-keeping circuit, the more will be reduced the load on the CPU.
Accordingly, it is an object of this invention to provide a time data processing apparatus wherein both the time-counting by a time-keeping circuit and various arithmetic operations using time data from the time-keeping circuit can be easily accomplished.